Biomedical Engineering Reference
In-Depth Information
Fig. 6.2. Illustration of the effect of using a blunt probe. These two images are of the same sample,
and both are 1.5
m
1.5
m
40 nm. The image on the left was taken with a sharp probe, the
image on the right with a blunt probe. The sample is BOPP, a useful sample to characterize the
sharpness of IC-AFM probe tips, see Appendix A9.
0
1
m
m
2
m
m
3
m
2
m
m
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Fig. 6.3. Example of features appearing smaller due to the use of a blunt probe. Left: SEM image of
a test pattern of squares (NT-MDT grating TGX, see Appendix A). The sides of the squares are all
equal. B: AFM image of the test pattern. Because the probe is not sharp, the test pattern squares
appear much smaller than they should, and appear as rectangles instead of squares.
6.1.2 Contaminated or broken probes
Contamination of AFM probes is quite common, and scanning certain samples leads to
dirty probes more quickly than others. In particular, biological or other soft samples, or
any sample with loose material at the surface, tend to contaminate probe tips quickly,
leading to image degradation [378]. On the other hand, breaking of the AFM probe is less
common, but still occurs, mainly when the probe accidentally touches the sample outside
of feedback control. The reason these two problems are described together is than they can
give very similar results. When imaging a sample with a broken or dirty probe, the
resulting images often contain features with unexpected shapes, due to convolution of
the misshapen tip with the sample features. Examples are shown in Figure 6.4. Any
repeating patterns within the images, which are not expected based on what is known of
the sample, are likely to be due to a broken or contaminated probe.
